Very high resolution stacked oled display

ABSTRACT

A full-color display and techniques for fabrication thereof are provided. The display includes first and second continuous independently addressable organic emissive layers disposed over a single substrate or between two substrates or portions of a flexible substrate. The use of continuous emissive layers of a limited number of colors allows for a relatively high resolution display to be achieved without the use of fine metal masks or similar components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/658,752, filed Jul. 25, 2017, which is a non-provisional of U.S.Patent Application Ser. No. 62/367,934, filed Jul. 28, 2016, the entirecontents of each of which is incorporated herein by reference.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to full-color display panels and devicessuch as organic light emitting diodes and other devices, including thesame.

Background

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin US Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

As used herein, a “full color” display or device is one that is capableof producing a full spectrum of visible light by having addressablesub-pixels of at leat three primary colors. The light produced by adisplay may not be the same color or colors as the light initiallyemitted by one or more emissive materials, layers, or regions of thedevice. For example, a conventional white-emitting OLED generally is notconsidered a “full color” device unless it is used in conjunction withother components, such as color filters, that convert the white lightproduced by the device into individual colors.

As used herein, a “red” layer, material, region, or device refers to onethat emits light in the range of about 580-700 nm; a “green” layer,material, region, or device refers to one that has an emission spectrumwith a peak wavelength in the range of about 500-600 nm; a “blue” layer,material, or device refers to one that has an emission spectrum with apeak wavelength in the range of about 400-500 nm; and a “yellow” layer,material, region, or device refers to one that has an emission spectrumwith a peak wavelength in the range of about 540-600 nm. In somearrangements, separate regions, layers, materials, regions, or devicesmay provide separate “deep blue” and a “light blue” light. As usedherein, in arrangements that provide separate “light blue” and “deepblue”, the “deep blue” component refers to one having a peak emissionwavelength that is at least about 4nm less than the peak emissionwavelength of the “light blue” component. Typically, a “light blue”component has a peak emission wavelength in the range of about 465-500nm, and a “deep blue” component has a peak emission wavelength in therange of about 400-470 nm, though these ranges may vary for someconfigurations. Similarly, a color altering layer refers to a layer thatconverts or modifies another color of light to light having a wavelengthas specified for that color. For example, a “red” color filter refers toa filter that results in light having a wavelength in the range of about580-700 nm. In general there are two classes of color altering layers:color filters that modify a spectrum by removing unwanted wavelengths oflight, and color changing layers that convert photons of higher energyto lower energy. Two components, such as two emissive regions, layers,materials, or devices are considered to have the “same color” if theyemit light having a peak wavelength within the same range as disclosedherein. For example, two emissive regions may both be described as “red”and thus described as having the “same color” if both regions emit lighthaving a peak wavelength in the range of about 580-700 nm.

SUMMARY OF THE INVENTION

In an embodiment, a full-color display is provided that includes a firstcontinuous independently addressable organic emissive layer and a secondcontinuous addressable organic emissive layer disposed over the firstcontinuous addressable organic emissive layer. The emissive layers maybe any desired color, such as a blue emissive layer and a yellowemissive layer. The display may include exactly two independentlyaddressable organic emissive layers, and/or continuous organic emissivelayers of exactly two colors. The first and second continuousaddressable organic emissive layers may be concurrently independentlyaddressable. A conductive layer, which may be transparent with anabsorption of 30% or less within the 450-700 nm visible range, may bedisposed between the first and second emissive layers to provideelectrical connections for a plurality of sub-pixels. An electrodelayer, which may include multiple electrodes, may be disposed below thefirst continuous independently emissive layer. One or more of theelectrodes may include projections that extend between the electrode andthe conductive layer. The plurality of electrodes may define a pluralityof sub-pixels. For example, each electrode may define a sub-pixel.Sub-pixels may have different optical path lengths, such as where adifferent path length is used for different colors of sub-pixels. Apatterned third organic layer may be disposed over at least a portion ofthe electrodes in the electrode layer. The patterned emissive layer mayinclude an emissive material having a peak wavelength of a differentcolor than a peak wavelength of the patterned first continuousaddressable organic emissive layer. One or more color altering layersmay be used. For example, a first color altering layer disposed in astack with a first region of the first continuous addressable organicemissive layer, and/or a second color altering layer disposed in a stackwith a second region of the first continuous addressable organicemissive layer that is distinct from the first region of the firstcontinuous addressable organic emissive layer. Each sub-pixel within thedevice may have a separate backplane circuit, or multiple sub-pixels maybe electrically connected to and controlled by a common backplanecircuit. The display may have less than one backplane circuit persub-pixel. The display may include two backplanes, with each of thefirst and second continuous addressable organic emissive layers being insignal communication with, and controlled by, one backplane. A coloraltering layer, such as a deep blue color altering layer, may bedisposed in a stack with the one of the continuous addressable organicemissive layers and not with the other. The display may includesub-pixels of at least four colors. An outcoupling component may beoptically coupled to at least a portion of the display and disposed in astack with at least one of the electrodes, such as in a stack with onecolor of sub-pixel. The display may be incorporated into a wide varietyof devices, such as a flat panel display, a computer monitor, a medicalmonitor, a television, a billboard, a light for interior or exteriorillumination and/or signaling, a heads-up display, a fully or partiallytransparent display, a flexible display, a laser printer, a telephone, acell phone, a tablet, a phablet, a personal digital assistant (PDA), alaptop computer, a digital camera, a camcorder, a viewfinder, amicro-display, a 3-D display, a virtual reality or augmented realitydisplay, a vehicle, a large area wall, a theater or stadium screen, asign, or the like. In a specific configuration, the display may includea first electrode layer that includes a plurality of first electrodes, aconductive layer disposed over at least one of the plurality of firstelectrodes, the conductive layer having a plurality of verticalprotrusions that extend above an upper boundary of the first continuousindependently addressable organic emissive layer, a second electrodelayer disposed between the first and second continuous independentlyaddressable organic emissive layers, where the plurality of verticalprotrusions extend into the second electrode layer; and a thirdelectrode layer disposed over the second organic emissive layer; inwhich electrodes within each of the first, second, and third electrodelayers are independently addressable.

In an embodiment, a method of fabricating a full-color display isprovided. The method may include disposing a first electrode layercomprising a plurality of first electrodes over a substrate; fabricatinga conductive layer comprising a plurality of vertical protrusions overat least one of the plurality of first electrodes; fabricating a blanketfirst organic emissive layer disposed over at least a portion of thefirst plurality of electrodes, wherein the plurality of verticalprojections extend above an upper boundary of the first organic emissionlater; fabricating a blanket second organic emissive layer disposed overthe first organic emissive layer; fabricating a second electrode layerdisposed between the first and second organic emissive layers, whereinthe plurality of vertical protrusions extend into the second electrodelayer; and fabricating a third electrode layer disposed over the secondorganic emissive layer. Electrodes within each of the first, second, andthird electrode layers may be independently addressable via anelectrical connection external to the arrangement. The method mayfurther include fabricating a patterned third organic emissive layerdisposed over at least a portion of the first plurality of electrodes,wherein the patterned third organic emissive layer comprises an emissivematerial having a peak wavelength of a different color than a peakwavelength of the patterned first organic emissive layer. The patternedthird organic emissive layer may not be disposed over the patternedfirst organic emissive layer.

In an embodiment, a full-color display is provided that includes a firstcontinuous independently addressable organic emissive layer and a secondcontinuous independently addressable organic emissive layer disposedover the first continuous addressable organic emissive layer, in whichthe first and second continuous addressable organic emissive layers areconcurrently independently addressable. The first continuousindependently addressable organic emissive layer may be disposed over afirst substrate, and the second continuous independently addressableorganic emissive layer may be disposed over a second substrate. Thefirst substrate may be disposed over the second substrate. The firstemissive layer may be disposed over a first portion of a flexiblesubstrate, and the second continuous independently addressable organicemissive layer may be disposed over a second portion of the flexiblesubstrate, i.e., the first and second substrates may be a singlecontinuous flexible substrate. The first independently addressableorganic emissive layer may be disposed over the second independentlyaddressable organic emissive layer, such as where two substrates areplaced in a stacked configuration, or where a single flexible substrateis curved or bent to place one emissive layer over the other. Thedisplay may include exactly two independently addressable organicemissive layers. An electrode layer including a plurality of electrodesmay be disposed below the first continuous independently emissive layer.The electrodes may define a plurality of sub-pixels, such as where eachelectrode defines a single sub-pixel. Different sub-pixels within thedisplay may have different optical path lengths. The display may includea single set of data lines. The display may include organic emissivelayers of exactly two colors. One or more color altering layers may bedisposed in a stack with regions of the first continuous addressableorganic emissive layer The display may have less than one backplanecircuit per sub-pixel. The display may have a first backplane and asecond backplane, with the first continuous addressable organic emissivelayer being in signal communication with, and controlled by, the firstbackplane and the second continuous addressable organic emissive layerbeing in signal communication with, and controlled by, the secondbackplane. The first and second emissive layers may comprise blue andyellow, or yellow and blue emissive materials, respectively. The firstcontinuous addressable organic emissive layer may be disposed between afirst backplane and the second continuous addressable organic emissivelayer, and the second continuous addressable organic emissive layer maybe disposed between a second backplane and the first continuousaddressable organic emissive layer. The display may be incorporated intoa variety of devices, such as a flat panel display, a computer monitor,a medical monitor, a television, a billboard, a light for interior orexterior illumination and/or signaling, a heads-up display, a fully orpartially transparent display, a flexible display, a laser printer, atelephone, a cell phone, a tablet, a phablet, a personal digitalassistant (PDA), a laptop computer, a digital camera, a camcorder, aviewfinder, a micro-display, a 3-D display, a virtual reality oraugmented reality display, a vehicle, a large area wall, a theater orstadium screen, a sign, or the like.

In an embodiment, a method of fabricating a full-color display isprovided, which includes fabricating a first continuous independentlyaddressable organic emissive layer of a first color over a firstsubstrate; fabricating a second continuous independently addressableorganic emissive layer of a second color over a second substrate,wherein the second color is different than the first color; and placingthe first substrate over the second substrate. The second substrate maybe the same substrate as the first substrate, and the step of placingthe first substrate over the second substrate may include bending thefirst substrate at a point between the first and second continuousindependently addressable organic emissive layers. Alternatively, thesecond substrate may be physically separate from the first substrateprior to placing the first substrate over the second substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIGS. 3A, 3B, 3C, 3D, 3E, 3F, 3G, and 3H show example fabricationprocess steps and resulting structures for a display architectureaccording to embodiments of the invention.

FIG. 4 shows a top schematic view of a portion of a full-color OLEDdisplay panel according to an embodiment of the invention.

FIG. 5 shows an example of a device having two substrates according toan embodiment of the invention.

FIG. 6 shows an example pixel arrangement in which a deep blue sub-pixelis shared among four pixels according to an embodiment of the invention.

FIG. 7A shows a top schematic view of a single flexible substrate havingtwo emissive stacks or layers disposed thereon according to anembodiment of the invention.

FIG. 7B shows a side view of the structure shown in FIG. 7A, with thesubstrate folded or bent to provide a structure as shown in FIG. 5,according to an embodiment of the invention.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-I”), which are incorporated byreference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink-jet and OVJP. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. Such consumer products would include anykind of products that include one or more light source(s) and/or one ormore of some type of visual displays. Some examples of such consumerproducts include flat panel displays, computer monitors, medicalmonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads-up displays, fully or partiallytransparent displays, flexible displays, laser printers, telephones,cell phones, tablets, phablets, personal digital assistants (PDAs),laptop computers, digital cameras, camcorders, viewfinders,micro-displays less than 2 inches diagonal, 3-D displays, virtualreality or augmented reality displays, vehicles, video walls comprisingmultiple displays tiled together, theater or stadium screens, and signs.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 C. to 30 C., and more preferablyat room temperature (20-25 C.), but could be used outside thistemperature range, for example, from −40 C. to +80 C.

Recent OLED research has developed techniques for fabricating afull-color OLED display panel using separately-addressable yellow andblue OLED stacks. In such techniques, one high resolution masking stepmay be used to ensure that a middle electrode can be externally andindependently driven from the backplane. Such a display architecture maybe useful for high resolution OLED displays which require long displaylifetimes, high brightness and low power consumption. Typically, red andgreen sub-pixels are achieved through the use of color filters. Thisapproach generally has several performance advantages when compared to aconventional arrangement that uses a white OLED stack and multiple colorfilters. Color filters in a conventional white stack generally reducelight output for each color, thereby reducing the display efficiency andpotentially also the blue lifetime because the blue fill factor iseffectively relatively low, so increased luminance is needed tocompensate. It also may be difficult to optimize a white top emissioncavity for all three colors, thereby lowering performance. Blue colorfilters also typically cannot completely cut out deep green, so onlyyellow-green emitters are used, further lowering the efficiency of anydeep green sub-pixels.

Disclosed herein are techniques and arrangements that use a limitednumber of emissive depositions, while avoiding the need for highresolution masking. In embodiments disclosed herein, multiple OLEDstacks may be continuous across the active layer. For example, in ayellow- and blue-based devices, both the yellow and blue depositions maybe continuous across the active area of a full-color display. To achievesuch an arrangement, a patterned metal such as Al, Ag, or the like maybe deposited on anodes dedicated to the blue sub-pixels. Withappropriate heating or other processing, spikes will form that willelectrically connect the blue anodes to the middle transparentconductive electrode. For example, it has been found that for a single300° C. Al deposition, approximately 30-50% of the total hillockpopulation were at least 100 nm in height; approximately 10% were atleast 200 nm; and less than 1% were equal to or greater than 500nm.Further coatings of metal may be made over the initial features toincrease the size and height.

Alternatively or in addition, metal nanorods, such as Au or Ag nanorods,may be formed on the surface of a sub-pixel electrode. For example, inan embodiment such nanorods may be fabricated or otherwise disposed onthe blue anode, i.e., the anode controlling the blue sub-pixel. Thenanorods can be formed by a number of methods, including lithographicmasking and solution printing techniques such as ink jet printing. Ineither case, the density and height of the nanorods is predictable inthe height desired for fabricating the shorting layer, and can be wellcontrolled and determined. Dimensions of nanorods known in the artindicate that they may be used to connect the blue anode to the middleconductive transparent electrode reliably without shorting to the topcathode.

After the blue anode is connected to the central conductive transparentelectrode, additional steps and/or structures may be desirable toprevent the hillocks, rods or spikes, from shorting the centralelectrode to the cathode, i.e., by shorting the upper blue OLED stack.Various strcutures and techniques may be used to prevent such shorting.

For example, a thick HTL may be fabricated or placed in the upper bluestack. to prevent the metal spikes from the blue anode from reaching thecathode. To avoid a voltage increase, the HTL may be conductivity doped.In such a configuration, the HTL thickness may be 10-300 nm or more.

As another example, a relatively thin, continuous, medium-resistancecathode may be used in combination with very low resistance buslinesthat are patterned over the substrate away from the blue anodes. Forexample, the sheet resistance may be greater than about 1 KΩ/square andless than about 100 KΩ/square. If the blue anode does short through tothe cathode, this arrangement will act as an effective resistor betweenthe short and a low resistance cathode bus line, thereby localizing theeffect of the short to one set of blue pixels. In many cases this not bevisually apparent given the eye's low-resolution sensitivity to blue.

As another example, a non-conductive organic or inorganic film may beevaporated over the display through a mask to coat the areas of thedisplay over the blue anode connections. The evaporated region may belarger than the blue anode, but may be a relatively small portion of theoverall pixel area of a display, such as no more than about 20% of thepixel area. A continuous conductive cathode also may be fabricated overthe display. The upper blue OLED formed over the blue anode contact willtherefore have no electrical connection to the cathode, therebypreventing shorting. The evaporated non-conducting film may besufficiently thick to physically prevent the anode spikes fromconnecting with the cathode. The particular mask required for such aprotective evaporation generally will be less critical than the maskthat would be needed for a conventional emissive layer patterning. Forexample, the mask may have only small openings relative to the pixelsize. Furthermore, there may be no need to prevent or address overspillfrom one ELM to a neighbor as in a conventional FMM process, so the maskcan be thicker and the openings will not need to be tapered.Accordingly, masks used in such a process will be cheaper, less complex,and longer-lived with less of a cleaning requirement than would beexpected for conventional emissive depositions. Alternatively, a processsuch as LITI, OVJP, or the like may be used to provide a similar film,without the use of a masking step.

FIGS. 3A-3G show an example fabrication process and associatingstructure according to an embodiment of the invention. In FIG. 3A, apatterned layer electrode layer, such as an anode layer, is deposited orotherwise disposed over a substrate 300. The electrode layer may includemultiple sub-pixel electrodes, such as for providing electrical contactto each of the blue, red, green, and/or yellow sub-pixels, e.g.,sub-pixel anodes 301, 302, 303, 304, respectively. Each sub-pixelassociated with the sub-pixel electrodes 301-304 may be individuallyaddressable. For example, the electrodes 301-304 may each be connectedto a backplane circuit for active-matrix addressing. Alternatively,multiple electrodes 301-304 within a single pixel or within multiplepixels may be connected to a common backplane circuit. Forbottom-emission devices, red and green color-altering layers, such ascolor filters, also may be fabricated vertically adjacent to, orotherwise in a stack with, the red and green sub-pixel electrodes 302,303. The electrode layer may be a patterned layer, i.e., one thatincludes designated and areas of electrode material that repeat in a setpattern across the area of a substrate. Alternatively or in addition,the electrode layer may include one or more blanket depositions ofelectrode material that are separated by previously-defined insulatingregions. More generally, any suitable arrangement and technique ofsub-pixel electrode deposition and/or fabrication may be used. Althoughthe drawings provided herein show sub-pixels for one or a small numberof pixels, one of skill in the art will readily understand that thearrangement may be repeated and extended to provide an arbitrarily largeOLED panel including any desired number of pixels.

In FIG. 3B, a metal layer 310 may be fabricated over one color ofsub-pixel electrodes, such as the blue electrodes 301. Upon heating orother treatment, the metal layer may form into one or more hillocks thatextend away from the sub-pixel electrode 301. Alterantively or inaddition, metal nanorods or similar structures may be fabricated ordisposed over the electrode 301. FIG. 3C shows a schematicrepresentation of the metal layer after heating or other treatment tocause such hillocks. The metal layer 310 may be altered, such as throughheat treatment, to include hillocks, or similar structures may befabricated or disposed over the sub-pixel electrode 301 as previouslydisclosed.

A continuous or “blanket” layer of emissive material may be disposedover the layer of sub-pixel electrodes, such that the hillocks or otherprotrusions extend through the material. The layer also may includeadditional non-emissive materials, such as transport layers. The layermay be a continuous layer or series of continuous layers that extends,for example, unbroken across the entire region of the substrate overwhich all sub-pixel electrodes for one or more pixels are positioned,i.e., across the entire active area of a portion of a display associatedwith one or more pixels. For example, a continuous emissive layer mayextend across an entire OLED display panel without breaks. FIG. 3D showssuch an arrangement in which a blanket yellow layer 315 is disposed overthe sub-pixel electrodes 301, 302, 303, 304. The protrusions of themetal layer 310 disposed over the blue sub-pixel electrode 301 extendabove the continuous blanket yellow layer 315. The continuous emissivelayer 315 and any associated non-emissive layers may be transparent orsemi-transparent. For example, the emissive layer 315 may have anabsorption of not more than about 30% in the 450-700 nm wavelengthrange.

A conductive layer or layers may then be disposed over the blanketemissive layer 315 to provide a middle or central electrode. FIG. 3Eshows a configuration in which a middle electrode 320 is disposed overthe blanket emissive layer 315. The metal protrusions 310 extend throughthe blanket emissive material layer 315 to contact the middle electrode320, thereby shorting the portion of the blanket emissive layer over onesub-pixel electrode 301. In this example, the region over the bluesub-pixel electrode 301 is shorted between the anode and the conductivelayer 320. This effectively extends the blue sub-pixel electrode abovethe blanket yellow layer 315 without requiring the use of a mask aswould be the case in conventional techniques and arrangements. Theconductive layer 320 may be transparent; for example, it may have anabsorption of not more than 30% in the visible 450-700 nm wavelengthrange.

One or more additional blanket emissive material layers may be disposedover the middle electrode. As previously disclosed, additionalnon-emissive layers such as transport layers that operate in conjunctionwith the emissive layer also may be disposed over the middle electrode.More generally, although emissive layers are shown as single layers forease of illustration, it will be understood that the emissive layerstypically will be implemented in emissive stacks, i.e., with associatedelectrodes and other organic layers such as transport layers, blockinglayers, and the like, as disclosed with respect to FIGS. 1 and 2. Forexample, a blanket layer of emissive material of the same color as thesub-pixel shorted in FIG. 3E may be disposed over the electrode. Such anarrangement is shown in FIG. 3F. In this example, a blanket layer ofblue emissive material 360 is disposed over the middle electrode 320.Notably, as with the yellow blanket layer 315, the layer may bedeposited without the use of a mask. The particular colors of emissivelayers disclosed and illustrated herein are illustrative only, andvarious other combination may be used. For example, the blanket layer315 may be a blue emissive layer and the blanket layer 360 may be ayellow emissive layer. Furthermore, combinations other than yellow andblue for the blanket continuous emissive layers 315, 360 may be used.For top-emission devices, one or more color filters 325, 330 may bedisposed over the associated sub-pixel electrodes 302, 303,respectively. For example, a red color filter 325 may be disposed over ared sub-pixel electrode 302, and a green sub color filter 330 may bedisposed over a green sub-pixel electrode. The color filters 325, 330may be incorporated into the blanket layer 360 or disposed over theblanket layer 360 using techniques known in the art. One or more thinfilm encapsulation layers also may be fabricated or otherwise disposedover one or more of the sub-pixels, such as in a stack either over orunder one or more of the color filters.

FIG. 3G shows a complete device according to embodiments of theinvention, including a blanket top electrode 340 such as a cathode.

As previously disclosed, in some cases it may be desirable to includeadditional features to further prevent shorting of the blue sub-pixelabove the associated sub-pixel electrode. For example,

FIG. 3H shows an example in which a non-conducting organic layer 350 orsimilar structure is disposed over the blue sub-pixel electrode 301prior to the blanket cathode 340 being disposed over the pixel.

Each of the blanket emissive layers 310, 360 may become part of OLEDsub-pixels that are independently addressable, and as such may bereferred to as “independently addressable” layers. As used herein, alayer or region of emissive material is “independently addressable” ifit can be addressed separately and independently from any other layer orregion of emissive material within a particular device or portion of adevice. In some cases an “independently addressable” layer may includemultiple sub-layers or multiple emissive materials. For example, ayellow emissive layer may include red and green emissive materials, orred and green emissive sub-layers, such as where the yellow layer isformed by first depositing a green or red sub-layer, followed by thecomplementary red or green sub-layer. Within such layers, it is notpossible to individually activate the sub-layers or individual emissivematerials separately from the other sub-layers or materials.Accordingly, while the emissive layer may be independently addressable,each sub-layer or material is not independently addressable.

However, within a device as disclosed herein, the separate continuousblanket layers 310, 360 may be independently addressable due to thepresence of the middle electrode 320. This configuration is in contrastto a device such as a white device that includes multiple layers thatcannot be independently addressed. For example, a conventional stackedwhite device may include red, green, and blue emissive layers that arecontrolled by a single set of electrodes. Accordingly, the red, green,and blue emissive layers within the stacked white device cannot beindividually activated separately from one another and, therefore,cannot be independently addressable. More generally, conventional whitedevices do not include any individually addressable layers and thedevice may only be addressed as an entire white-emitting device.

In embodiments disclosed herein, an “independently addressable” layermay include multiple portions arranged over a plurality of electrodes,each of which portion is independently addressable. Such portions aredistinguished from, for example, the sub-layers of a white device,because they are associated with separate and independent electrodes.For example, FIGS. 3A-3H show sub-pixels that emit red and green lightusing color filters 325, 330. Each sub-pixel includes an associatedsub-pixel electrode 302, 303, respectively, disposed in the electrodelayer. Each of the electrodes 302, 303 is controllable independently ofthe other, and independently of other electrodes in the pixel and thedevice. Accordingly, those portions of the blanket continuous yellowlayer 360—i.e., the red and green sub-pixels—are independentlyaddressable relative to one another.

In some embodiments, spatial resolution techniques may be used to reducethe relative number of color filters used, such as by sharing one anodeof a particular color among multiple pixels. For example, following theprevious examples in which yellow and blue blanket layers are used incombination with red and green color filters to achieve red, green,blue, and yellow sub-pixels, blue anode contacts may be shared amongfour sub-pixels. Because the eye has lower spatial resolution to blue,it may be desirable for one blue anode connection, and therefore oneblue sub-pixel, to be shared between multiple pixels. This may allow formore efficient arrangements with minimal or no loss in apparent qualityor resolution.

An example of such an arrangement is shown in FIG. 4. In this example,blue anode contacts 450 are shared among the blue sub-pixels of fourpixels as shown. The device includes blue sub-pixels 410, red sub-pixels420, green sub-pixels 430, and yellow sub-pixels 440. Such a device mayhave the layered structure shown and described with respect to FIGS.3A-3H or variations thereof. Notably, the structure may be fabricatedwithout the use of fine masks as previously disclosed.

Although described with respect to top-emitting examples, embodimentsdisclosed herein may include both bottom and top emission displayarchitectures. Regardless of the specific architecture used, thethicknesses of the yellow and blue emissive layers and/or the positionof the respective emissive layers relative to the bottom and topcontacts may be tailored to achieve favorable optical cavities for eachcolor. For example, the thicknesses of the various layers disclosed maybe tailored to provide a microcavity suitable for providing deep blueemission.

More generally, some emodiments may include one or more organic layers,which may be patterned to correspond to the sub-pixel electrodes of theelectrode layer as previously disclosed. Such layers may be configuredto provide a desired optical path length for any of the sub-pixels ofthe device. For example, in some embodiments, the optical path lengthfor a particular color sub-pixel may be selected to provide a tunedcolor for the sub-pixel. As a specific example, the optical path lengthfor a blue sub-pixel may be selected to provide deep blue emission.Furthermore, organic material used to create a particular optical pathlength may be emissive or non-emissive. As previously disclosed, suchmaterial may be a HTL or similar material. Alternatively or in addition,emissive material may be used, for example to augment the emission of aparticular sub-pixel. Different sub-pixels may have different opticalpath lengths within a pixel or a device.

Notably, embodiments disclosed herein may include emissive layers of notmore than two colors. For example, the arrangement shown in FIGS. 3A-3Hincludes only blue and yellow emissive layers. In this exampleconfiguration, red and green sub-pixels are provided by a combination ofthe yellow emissive layer and suitable color filters or other coloraltering components. As noted above, although an emissive layer such asa yellow emissive layer may include sub-layers, such as green and redsub-layers, the yellow layer is still considered a single emissive layeras disclosed herein because the arrangement of components does not allowfor the green or red sub-layers to be activated separately from theother. That is, the yellow emissive layer emits yellow light only.Although this light may be converted to red or green light through theuse of color filters, it is not possible for the blanket yellow layer toemit green or red light separately without the use of a color alteringcomponent. A configuration as disclosed herein that includes only twocontinuous organic emissive layers while still providing a full-colordevice may be desirable over conventional arrangements since the deviceis much less complex, and does not require the use of masking techniquesto fabricate the device.

In some embodiments, an outcoupling component may be optically coupledto one or more of the sub-pixels of the device. For example, a microlensarray may be disposed above or below one or more sub-pixels, dependingupon whether the device is a top- or bottom-emitting device, to furtherincrease the amount of light emitted by the sub-pixel. As used herein,an “outcoupling component” refers to a component that outcouples lightfrom an OLED. To perform outcoupling, a component must, when opticallycoupled to an emissive region of an OLED either directly or indirectly,result in more light exiting the OLED than otherwise would exit the OLEDin the absence of the outcoupling component. Examples of outcouplingcomponents include microlens arrays of any size, shape, and arrangement.

Embodiments disclosed herein, such as those shown in FIGS. 3-4, may bedriven using driving schemes that are particularly adapted to the devicearrangement. For example, the middle conductive layer 320 shown in FIG.3 may act as a cathode for some sub-pixels in the device, and as ananode for other sub-pixels in the device. A drive scheme for such anarrangement may alternate between addressing each organic emissivelayer, such that the sub-pixels for which the conductive layer acts as acathode are addressed sequentially, i.e., non-concurrently, with thesub-pixels for which the conductive layer acts as an anode. Examples ofsuitable driving schemes are disclosed in U.S. application Ser. No.15/172,888, filed Jun. 3, 2016, and U.S. application Ser. No.15/169,027, filed May 31, 2016, the disclosure of each of which isincorporated by reference in its entirety.

Embodiments disclosed above with respect to FIGS. 3-4 use twocontinuous, independently addressable emissive layers, for example, oneyellow and one blue. Both emissive layers are unpatterned at the pixellevel and are disposed in separate planes within a devce. In someembodiments, such an arrangement may be used to provide high to veryhigh resolution displays with resolutions of, for example, 1,000 dpi ormore. Pixel dimensions for such displays typically will be will be lessthan about 25 microns. To avoid parallax issues, the planes in which theemissive layers are disposed may be located relatively close to oneanother, for example, with a separation of not more than about 25 μm inthe z-direction, relative to the display surface being an xy plane,i.e., normal to the substrate surface. Many substrates are thicker than100 um, which indicates that either the two emissive planes should bestacked on the same side of a single substrate, or placed on twodifferent substrates, joined together with the sides onto which theemissive layers have been deposited facing each other.

In some cases, such as for small-area, high resolution displays forapplications such as virtual reality or augmented reality, the substrateand backplane cost may be only a small fraction of an overall displaycost in comparison to the costs of OLED depositions, row and columndrivers, timing controller circuits, video processing, circularpolarizers and touch panels, and other system components.

In this and other situations, a high resolution display may be providedusing multiple substrates. FIG. 5 shows an example of such a device. Thedevice includes two substrates 500, 501, on which are deposited twocontinuous, individually-addressable organic emissive layers 550, 560.As previously disclosed, these blanket layers 550, 560 may be, forexample, blue and yellow emissive layers. Although single layers areshown in FIG. 5 for ease of illustration, it will be understood that theemissive layers typically will be implemented in emissive stacks, i.e.,with associated electrodes and other organic layers such as transportlayers, blocking layers, and the like, as disclosed with respect toFIGS. 1 and 2. Sub-pixels of other colors, such as red and green, may beprovided through the use of color filters 530, 540 or other coloraltering layers, or by the use of varied optical path lengths within thedevice as previously disclosed. In an example device, the unpatternedyellow emissive layer is deposited on to one substrate, and anunpatterned blue emissive layer is deposited on to a second substrate.Each substrate 500, 501 may have its own associated backplane 570, 520,respectively. In comparison to a structure as described with respect toFIG. 3, there are no additional OLED costs associated with the deviceshown in FIG. 5. However, there may be additional or different costs dueto the use of two backplanes and possibly only one set of column driversfor example as described with respect to FIG. 7. Each blanket emissivelayer 550, 560 may have a thin film or other suitable encapsulation 551,561. The color filters 530, 540 disposed on one substrate 501 may beselected to complement the color emitted by the blanket emissive layerdisposed on the other substrate 560. For example, for a yellow-emittingblanket emissive layer 560, the color filters 530, 540 may be red andgreen, so as to provide a full-color device having 3, 4, or 5sub-pixels.

As further described herein, in some embodiments a color filter 510 maybe used that is the same or a similar color as the associated emissivelayer 550. For example, the color filter 510 may be a deep blue colorfilter that converts blue or light blue light emitted by the blanketemissive layer 550 into deep blue light that is emitted from the deviceat 590. As shown in FIG. 6 and as disclosed in further detail herein, insuch a configuration a portion of the blanket emissive layer 550 mayremain unfiltered, for example to provide light blue light, while aportion of the emissive layer is disposed in a stack with the colorfilter 510, such as to provide deep blue light.

In an embodiment, the two substrates 500, 501 may be disposed such thatthe independently-addressable emissive regions are facing each other. Inthis case, one one OLED stack 582 may be configured as a top-emittingdevice, and one stack 581 may be transparent. The combined light thuswill propagate in a single direction 590. Furthermore, if ablue-emitting stack is configured for top emission, then deep blueemitted light may be obtained by including a microcavity or color filterin the stack as previously disclosed and allowing the light to passthrough a transparent yellow-emitting stack. However, theyellow-emitting stack typically includes at least 3 sub-pixels (yellow,green and red) as previously described and shown in FIG. 3 and aspreviously described with respect to FIG. 5. The stack thus includessufficient circuitry for three sub-pixel circuits, which may reduce theoverall transparency of the system. As another example, theyellow-emitting stack may be configured for top emission. In this caseonly the transmission properties of the blue-emitting stack may be ofinterest to the final light output of the device. As described infurther detail herein, the blue-emitting stack may include only about1.25 sub-pixel circuits per pixel, as opposed to 3 sub-pixel circuitsfor a yellow-emitting stack, thus having a much reduced impact ondisplay transmission and aperture ratios.

In some embodiments, such as where a blue-emitting stack is configuredas a transparent stack, the blue emission may be insufficientlysaturated to meet color gamut or other requirements. Accordingly in somecases it may be advantageous to provide two blue sub-pixels, in whichthe color of the as-deposited blue emissive layer would be a light blue,and a deep blue is provided using a color filter, microcavity, or othercolor altering component. Because the deep blue is only used for a smallnumber of images, the resulting lower efficiency is not a significantconcern and the light blue may be used to render most images.Furthermore, because the human eye generally cannot resolve highresolution deep blue images, one deep blue sub-pixel may be shared amongmultiple pixels. An example of such a configuration is shown in FIG. 6.This arrangement includes a single deep blue sub-pixel 610 formedthrough a combination of portions of light blue sub-pixels 650 and acolor altering component such as a color filter. Each pixel alsoincludes separate sub-pixels for green (620), red (630), and yellow(640) emission. Each deep blue sub-pixel may be driven by a data lineshared between two rows of pixels, and driven by two consecutive scanlines. Video processing can be adjusted such that each deep blue pixelrepresents the average of four picture elements. Examples of suitablevideo processing techniques are disclosed in U.S. Published PatentApplication No. 2015/0349034, the disclosure of which is incorporated byreference in its entirety.

A range of thin film transistor backplane technologies may be used todrive a display arrangement as shown in FIG. 5. Both organic andinorganic devices may be used. Examples of suitable materials includelow temperature polycrystalline silicon (LTPS), carbon nanotubetransistors, oxide transistors, and the like. One consideration for veryhigh resolution displays is that the required transistors may occupy arelatively significant portion of the available pixel area, and anycomponents or conductors that are not transparent may impact theperformance of the device. Accordingly, top-emission OLED stackarrangments may be preferred, so that the OLED stack may be placed overthe TFT devices and circuits and thereby prevent the backplane fromlimiting the display aperture.

Another approach to reduce the area occupied by the backplane is toemploy a driving scheme as previously disclosed, in which multiplexingtechniques are used. This allows the device to include one sub-pixelcircuit per pixel, which also may improve display transmission.

Further improvements in display transmission for a transparent backplanemay be achieved by using transparent conductors for local interconnectswithin each pixel, where extremely low resistances are not required. Forpixel currents of a few microamperes, local resistances of a few kilohmscan be tolerated. In this case various transparent conductors used inthe art, such as ITO, IZO, or silver nanotubes, carbon nanotubes, or thelike, may be employed.

In some embodiments, such as to provide for high resolutionapplications, sub-pixel rendering (SPR) concepts may be applied aspreviously disclosed. For example, only one green or one red sub-pixelmay be used per pixel. Each pixel on one substrate will then have ayellow sub-pixel and either a green or red sub-pixel. This reduces thenumber of column drivers to 2 for that substrate, and either 1 or 1.5for the other substrate, depending on whether it is top emission (e.g.,deep blue) or bottom emission (e.g., light blue) with a shared deep bluesub-pixel. Accordingly, it may be possible to use either substrate asthe transparent substrate, due to the relatively small number of columndrivers required.

As previously disclosed with respect to FIG. 3, an arrangement as shownin FIG. 5 may include one or more patterned organic layers that providesa different optical path length for one or more sub-pixels. For example,non-emissive organic material may be placed in a stack with one or moreof the sub-pixels defined by the color filters 510, 530, 540 and/orother portions of the emissive stacks defined by the blanket emissivelayers, such as the unfiltered portion of the emissive layer 550 belowthe backplane 520 in FIG. 5. As with the arrangements described withrespect to FIG. 3, each cavity may be optimized for a specific colordepending upon the color desired for the specific sub-pixel.

In some embodiments, one or more of the sub-pixels may be a stackeddevice. For example, either of the blanket layers may be fabricated as astacked device that includes multiple emissive layers that are notseparately independently addressable. As a specific example, the bluesub-pixel may be a stacked device either by using a stacked device asthe blanket layer, or by fabricating an additional blue emissive layerin a stack with the blue sub-pixel electrode. Such additional emissivelayer or layers also may serve to provide a desired optical path lengthas previously disclosed.

In an embodiment, a device architecture as shown in FIG. 5 may include asingle set of column drivers. In such an embodiment, scan drivers mayscan each backplane in 50% of the frame time. Columns of both emissivestacks, e.g., emissive layers 550, 560 in FIG. 5, may be driven at thesame time, with only a single scan line on one backplane selected at anyparticular time.

In an embodiment, each backplane, e.g., backplanes 520, 570, may bedriven independently. As a specific example, in a device having blue andyellow blanket emissive layers as shown in FIG. 5, the backplane for theblue emissive layer may require only one data line per pixel for thelight blue sub-pixel, and half a shared data line for the deep bluesub-pixel as previously disclosed. These data lines may be driven fromdata drive components specifically dedicated to the blue-emittingbackplane. Alternatively or in addition, they may use common columndrivers as the red, green, and yellow sub-pixels, which may be formedfrom a blanket yellow emissive layer. Such a configuration may providelower-cost and -complexity devices than conventional arrangements,especially since simple conventional driver chips may be used. The scandriving circuits for the two devices (i.e., the blue- andyellow-emitting stacks) may be synchronized, so that in each frame timethe system may sequentially scan through all the scan lines disposed inthe first substrate, followed by all scan lines in the second substrate.

To minimize the package size into which a display can be placed,flexible substrates may be used to allow the ends to be bent back forconnections to be made behind the display. For a display architecturewith two backplanes as shown in FIG. 5, both displays can be bent in thesame direction. External connections may be made to opposite ends ofeach substrate, with the backplane that is being connected made longerthan the other backplane.

In an embodiment, the two emissive stacks (e.g., emissive layers 550,560 in FIG. 5 and associated layers) may be fabricated on a singleflexible substrate, such as a plastic substrate. Both emissive layers,or both entire emissive panels (e.g., yellow and blue emissive stackpanels as previously disclosed) may be fabricated at the same time onthe same substrate, for example, by using a very low resolution maskwhile still avoiding the need for a fine metal mask or other highresolution pixel patterning. FIG. 7A shows a top schematic view of asingle flexible substrate 700 on which two blanket emissive layers 710,720 are disposed. The layers may be, for example, the blue and yellowemissive layers or stacks 550, 560 as shown in FIG. 5. Each emissivelayer 710, 720 may be considered to be disposed over its owncorresponding substrate, although a single substrate is used in thefabrication process. To achieve a structure as shown in FIG. 5, onesubstrate may be bent over the other to align the emissive layers aspreviously disclosed. Data lines 730 may be disposed across bothemissive regions, and column drivers 740 may be disposed at one end ofthe common substrate or in any other desired location, includingexternal to the common substrate. FIG. 7B shows a side view of the samestructure, with the substrate folded or bent to provide a structure asshown in FIG. 5. As previously disclosed, each panel may beencapsulated, such as with a thin film encapsulation layer, prior tobending and assembly. Notably, driver costs may be reduced as only twocolumn drivers and column lines are required per pixel, and the pitch ofconnections to the data lines is increased from 3 connections per pixelto 2 connections per pixel. A single scan driver may be used to driveboth halves of the display sequentially as previously disclosed.Alternatively or in addition, only a single set of driver chips may beused, so the incremental cost and complexity of achieving double adisplay area will be less than that required for a single small highresolution display, as the cost of the backplane often is dominated byperipheral electronics, touch panels, and other components.

In an embodiment, both backplanes and substrates may be made transparentto achieve a fully transparent display, for example, one having anabsorption of not more than about 30% in the 450-700 nm wavelengthrange. However, due the non-symmetric nature of the resultant display,it may be desirable to separately optimize the optical characteristicsof each display side to prevent content appearing different in color,brightness, or the like when each side of the display is observed. Forexample, additional optical layers may be applied to one of the twodisplay sides or, more preferably, underneath the TFT circuitry of oneof the display sides. Alternatively or in addition, a second set of redand green color filters may be used so that both display surfacesinclude red and green color filters below the respective emissive layerplanes. As another example, red and green color filters may be appliedon both sides of the yellow emissive layer.

In an embodiment, a display architecture as disclosed herein may be usedfor a large area display. While costs for such displays typically aredominated by the backplane and OLED, studies indicate that the backplanemay be about 10%-15% of the module cost. Accordingly, using anarchitecture as disclosed herein for a large area display may beeconomical and may provide additional benefits. For example, as TVresolutions are relatively low, either substrate can be transparent,thereby allowing the other emissive layer (i.e., the one disposed on theother substrate) to benefit from a cavity design with little concern ofreducing pixel aperture ratios. As another example, although the use ofa second backplane generally may increase costs, it also will greatlyimprove display performance, especially with respect to color gamut,brightness and lifetime, which may be more desirable than the relativelysmall increase in cost and complexity for a large area display.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. A method of fabricating a full-color display comprising: disposing afirst electrode layer comprising a plurality of first electrodes over asubstrate; fabricating a conductive layer comprising a plurality ofvertical protrusions over at least one of the plurality of firstelectrodes; fabricating a blanket first organic emissive layer disposedover at least a portion of the first plurality of electrodes, whereinthe plurality of vertical projections extend above an upper boundary ofthe first organic emission later; fabricating a blanket second organicemissive layer disposed over the first organic emissive layer;fabricating a second electrode layer disposed between the first andsecond organic emissive layers, wherein the plurality of verticalprotrusions extend into the second electrode layer; and fabricating athird electrode layer disposed over the second organic emissive layer;wherein electrodes within each of the first, second, and third electrodelayers are addressable via an electrical connection external to thearrangement.
 2. The method of claim 1, further comprising: fabricating apatterned third organic emissive layer disposed over at least a portionof the first plurality of electrodes, wherein the patterned thirdorganic emissive layer comprises an emissive material having a peakwavelength of a different color than a peak wavelength of the patternedfirst organic emissive layer, and wherein the patterned third organicemissive layer is not disposed over the patterned first organic emissivelayer.
 3. The method of claim 1, wherein the conductive layer defines aplurality of sub-pixels.
 4. The method of claim 3, wherein a firstsub-pixel of the plurality of sub-pixels has a first optical path lengthand a second sub-pixel of the plurality of sub-pixels has a secondoptical path length different than the first optical path length.
 5. Themethod of claim 1, wherein the conductive layer is transparent.
 6. Themethod of claim 1, wherein the full-color display comprises continuousorganic emissive layers of exactly two colors.
 7. The method of claim 1,further comprising: disposing a first color altering layer in a stackwith a first region of the first organic emissive layer; and disposing asecond color altering layer in a stack with a second region of the firstorganic emissive layer that is distinct from the first region.
 8. Themethod of claim 7, wherein the full-color display comprises a pluralityof sub-pixels, each of which has a separate backplane circuit.
 9. Themethod of claim 7, further comprising arranging connecting sub-pixels toa common backplane circuit.
 10. The method of claim 9, wherein thefull-color display comprises less than one backplane circuit persub-pixel.
 11. The method of claim 1, further comprising: providing afirst backplane in signal communication with the first organic emissivelayer; and providing a second backplane in signal communication with thesecond organic emissive layer.
 12. The method of claim 1, wherein thefirst organic emissive layer comprises a yellow-emitting emissivematerial.
 13. The method of claim 1, wherein the second organic emissivelayer comprises a blue-emitting emissive material.
 14. The method ofclaim 13, further comprising disposing a deep blue color altering layerin a stack with the second organic emissive layer and not with the firstorganic emissive layer.
 15. The method of claim 1, wherein thefull-color display comprises sub-pixels of at least four colors.
 16. Themethod of claim 1, further comprising incorporating the full-colordisplay into a consumer device.
 17. The method of claim 16, wherein theconsumer device comprises at least one selected from the groupconsisting of: a flat panel display, a computer monitor, a medicalmonitor, a television, a billboard, a light for interior or exteriorillumination and/or signaling, a heads-up display, a fully or partiallytransparent display, a flexible display, a laser printer, a telephone, acell phone, a tablet, a phablet, a personal digital assistant (PDA), alaptop computer, a digital camera, a camcorder, a viewfinder, amicro-display, a 3-D display, a virtual reality or augmented realitydisplay, a vehicle, a large area wall, a theater or stadium screen, anda sign.